Electrical temperature indicating systems



1963 B. STEVENS 3,107,53 1

ELECTRICAL TEMPERATURE INDICATING SYSTEMS Filed Jan. 28, 1960 2Sheets-Sheet 1 IN VEN TOR.

figyam? 5261/6/75 Oct. 22, 1963 B. L. STEVENS ELECTRICAL TEMPERATUREINDICATING SYSTEMS 2 Sheets-Sheet 2 Filed Jan. 28, 1960 BY Z Z ATTORNEYUnited States Patent Ofifice Patented Oct. 22, 1963 3,187,531 ELECTRICALTEMPERATURE INDICATING SYSTEMS Bryce L. Stevens, Davison, Mich, assignorto General Motors Corporation, Detroit, Mich, a corporation of DelawareFiled Jan. 28, 196i), Ser. No. 5,201 4 Claims. (Cl. 73-362) Thisinvention relates to differential galvanometers and particularly toindicating systems of the electric telemetric type for showingtempertaure variations in installations such, for example, as inconnection with cooling systems of automobile engines.

An object of the present invention is to provide an improved low-costtemperature indicating system of the telemetric type.

A feature of the present invention is an indicating system employing twothermistors in a sender or in sending means for effecting thedifferential energization of two actuating coils in a data receivinggalvanometer unit or a e. g This and other features of the inventionwill now be de scribed in detail in the specification and then pointedout more particularly in the appended claims.

In the drawings:

FIGURE 1 is a front view of a gage with the dial and casting omitted;

FIGURE 2 is a side view of gage parts, some of the parts being shown insection as taken along the line 2-2 in FIGURE 1 and the dial being shownin dot and dash lines;

FIGURE 3 is a sectional view taken along the line 3-3 in FIGURE 2;

FIGURE 4 is a sectional view through sending means in the form of adouble thermistor; and

FIGURE 5 is a diagrammatic view of the circuit employed.

The term thermistor is herein used to denote a semiconductor having athermally variable resistivity. In the production of thermistors, theoxides of the transistion metals, combinations thereof,electro-ceramics, ferromagnetics and other materials have been useddependent upon the temperature and electrical characteristics desiredfor each installation.

When the temperature is constant, a thermistor reflects Ohms law at lowapplied voltage. With an increase in voltage a thermistor heats up andits electrical resistance decreases. A single thermistor has been usedheretofore in connection with a telemetric type gage but such use hasintroduced an additional electromagnetic coil and other complications.temperature changes as herein indicated, the present invention realizesthese advantages:

(1) A nearly linear scale is permitted for the gage;

(2) A strong pointer movement is attained;

(3) The gage structure may be symmetrical and therefore low in cost;

(4) Undistorted magnetic field gives gage stability;

(5) Identical coils eliminate errors due to ambient temperature changes.

The gage 10, as shown in the drawings, is similar in some respects, tothat of the gage shown in the United States Patent No. 2,178,108,granted October 31, 1939, in the name of Bruce H. Schwarze. The presentgage comprises a lower iron pole piece 11, a brass frame 12, a pointer14, an iron armature 16 which is adapted to rotate with the pointer, andtwo electro-magnetic coils 18 and 20 for actuating the armature andpointer with respect to a dial 22. A base 24 of insulating material(plastic) serves to insulate the frame 12 from the instrument casingwhich is not shown. Terminal studs 26, 28

In applying two thermistors for sensing and 30 (FIGURE 3) are providedand they pass through the base and are insulated from the frame 12.Three copper clad contact areas 32, 34 and 36 are formed on the frontside of the plastic base 24 and contact the heads of the studs. A fourthcopper contact area 38 is formed on the other or back side of theplastic base 24 and bears a tab 40. This fourth area serves as a groundconnection to the casing but is clear of the studs 26 and 28. In axialalignment with the studs 26 and 28 are two iron cores 27 and 29 held attheir rear ends by the lower pole piece 11 and which, at their frontends, are retained by the brass frame 12. These cores support two upperiron pole pieces 42 and 44 respectively. The pole pieces 11, 42 and 44form arcuate clearances or air spaces about the paths of the ends of thearmature 16. Rivets 46 and 47 (FIG- URE 3) pass through the base 24 andhold right angle conductor elements 48 and 50 for supporting aresistance 52 in the form of a coil shielded by two insulating strips 54and 56.

FIGURE 4 shows sending means 60 in the form of a double thermistor. Itcomprises a brass housing 62 hearing screw threads 64 by means of whichthe unit may be attached to an engine block. A plastic element 66 isheld within the housing 62 with a sealing washer 68 interposed betweenopposing shoulders formed on the two parts. Two terminals 70 and 72 aremoulded into the element 66. Coaxial vulcanized fiber sleeves 74 and 76are located within a chamber 78 defined in the housing. Two discs 79 and80 of semiconductor material forming the hearts of the therrnistors areurged toward the base of the housing by two coil springs 82 and 84respectively. The sleeve 74 is spaced from the inner wall surface of thechamber with one end abutting a metal grounding disc 86 surrounding thetube 76. The disc 86 contacts one surface of the semiconductor 79. Theother side of the disc 86 is insulated by a fiber Washer 90 from thesemiconductor 80. The spring 82 acts between an angle portion 94 of theterminal 70 and the semiconductor 79. The spring 84 acts between theinner end of the terminal 72 and the semiconductor disc 80 and isinsulated from the spring 82 and the discs 79 and 86 by the sleeve 76 aswell as by a transformer type oil or liquid substantially filling thechamber 78. This liquid could be ethylene glycol, glycerine or such typeof nonconductive heat transfer liquid. The liquid used should beeffective as a heat transfer medium between the housing 62 and the twothermistor semiconductor discs 79 and 80.

A source 96 of voltage supply is shown as a battery in FIGURE 5. Thenegative or positive side is grounded as at 98 and the other side isconnected in series with the coil 20 and the thermistor disc 79 by aLine 100, the stud 28, the copper area 36, the lines 100 and 104, thecopper area 34, the stud 30 and the housing 62. The copper area 36 alsoconnects the stud 28 to the conductor element 50 or one acting terminalof the resistor 52. The other terminal of the resistor includes theelement 48 contacting the copper coating 32 which is connected by thestud 26 and a line 108 to the terminal 72 leading to one side of thethermistor S0. The latter is grounded by the housing 62. The coating 32is also connected by a line 118 to one end of the coil 18. The other endof the latter is connected by a line 112 to the coating 38 forming aground with the gage casing.

In operation and assuming that the sending means 60 is subjected to arising temperature condition, the resistance of the thermistors or discs79 and 80 will decrease. The decrease in the resistance of thethermistor 80 causes an increase in the current through the resistance52 with a consequent increase in the voltage drop across the resistor52. This, of course,means that the potential at 26 is lowered with aresulting decrease in the current passing through the coil 18.

I claim:

1. An indicating system comprising sender means having two thermistorsarranged in parallel and adapted to be exposed to varying temperature, adifierential galvanorneter type gage having two actuating coils, avoltage source, a resistor connected in series with one of said coilsand one of said thermistors to said voltage source, said one coil andone thermistor being connected in parallel, and the other of said coilsbeing connected to said voltage source and in series with the other ofsaid thermistors.

2. An indicating system comprising sender means with two thermistorsarranged in parallel, a differential galvanometer type gage spaced fromsaid sender means as a separate indicating unit and having two actuatingcoils, a resistor in said indicating unit, one of said coils and one ofsaid therrnistors being connected in parallel to an output terminal ofsaid resistor, and the other coil and other thermistor being connectedin series.

3. An indicating system comprising a sending unit having two thermistorsand adapted to be exposed to a variable temperature in one locality, areceiving unit in the form of a galvanometer type gage adapted to bemounted in another locality, said gage unit having a pointer and twoactuating coils for said pointer, a re- 4- sistor, a voltage source, oneof said coils and said resistor being connected in series to saidvoltage source, one of said thermistors being connected in parallel withsaid one coil and in series with said resistor, and the other thermistorbeing connected in series with the other of said coils to said voltagesource.

4. An indicating system comprising two separately grounded thermistors,a gage having a pointer and two pointer actuating electromagnetic coils,a resistor, a voltage source, one of said coils and said resistor beingconnected in series to said voltage source, one of said thermistorsbeing connected in parallel with said one coil and in series with saidresistor, and the other of said thermistors being connected in serieswith the other of said coils to said voltage source.

References Cited in the file of this patent UNITED STATES PATENTS2,206,715 Burat et al July 2, 1940 2,567,756 Amsler Sept. 11, 1951FOREIGN PATENTS 379,703 Germany July 4, 1922 747,828 Great Britain Apr.18, 1956

1. AN INDICATING SYSTEM COMPRISING SENDER MEANS HAVING TWO THERMISTORSARRANGED IN PARALLEL AND ADAPTED TO BE EXPOSED TO VARYING TEMPERATURE, ADIFFERENTIAL GALVANOMETER TYPE GAGE HAVING TWO ACTUATING COILS, AVOLTAGE SOURCE, A RESISTOR CONNECTED IN SERIES WITH ONE OF SAID COILSAND ONE OF SAID THERMISTORS TO SAID VOLTAGE SOURCE, SAID ONE COIL ANDONE THERMISTOR BEING CONNECTED IN PARALLEL, AND THE OTHER OF SAID COILSBEING CONNECTED TO SAID VOLTAGE SOURCE AND IN SERIES WITH THE OTHER OFSAID THERMISTORS.